The heat of combustion of TNT is about 3400 kJ/mol (810 kcal/mol), or about
15 kJ (just under 4 kcal) per gram. This value is a good indicator of the
energy available from the detonation of TNT.

TNT requires a substantial amount of oxygen (42% oxygen by weight, or about
¾ gram oxygen per gram of TNT) for complete combustion. It is
commonly mixed with other explosives in various proportions depending on
the application. Presumably TNT is mixed with compounds which have extra
oxygen, for example ammonium nitrate or nitroglycerine. The energy released
by detonation of such mixtures will vary with the exact composition.

The Ordnance Shop is a good basic
source for information on explosives with military uses. More detailed
chemical information can be found at the TNT link given
above.

You answered 15 MJ/kg, based on complete combustion of TNT.
However, the questioner asked about energy of *detonation*, which I expect
is substantially less, since atmospheric oxygen is unavailable to complete
the combustion after the expansion of hot gases following detonation.

In fact, computations of nuclear weapons yields, asteroid strikes, and the
like (megatons, kilotons, etc.) use a value of about 4 MJ/kg.
You have: kg tnt
You want: kilojoules
* 4612.0705
/ 0.00021682236